The invention relates to a contact-filter block in accordance with the preamble of Patent Claim 1.
Such contact-filter blocks are used to construct trickling filters or rotating disc filters for the biological treatment of waste waters or other fluids. For this purpose, the contact-filter blocks are populated with a bio-mass, a so-called biological slime.
It is known to join a multiplicity of mutually adjacent tube sections having an outside surface structured in a net-like manner together to construct contact-filter blocks. The tube sections are joined by means of hot-tool welding by heating the end faces of the tube sections and applying pressure so that contact points of adjacent end faces of the tube sections fuse together and form joints.
As a result of this type of welding, material accumulations which constrict the (clear) internal cross-section of the tube sections are formed at the end faces of the tube sections. These cross-sectional constrictions in turn impede the flow through the contact-filter block in the longitudinal direction of the tube sections, thereby reducing the efficiency of such known contact-filter blocks.